Laser devices are used in the fields of processing machinery, medical equipment, measurement instruments, and the like. With such laser devices, there are cases where output light is reflected by an object to be processed or the like, and the reflected output light is input to the output terminal of the laser device. There has been known laser devices that monitor such reflected light, so as to reduce damage to the laser devices and grasp the condition of the object to be processed.
Patent Document 1 listed below discloses such a laser device. In this laser device, output light that has been reflected by an object to be processed and been input as reflected light to the output terminal is isolated and monitored before reaching the light source.